NEW PALEOCENE MAMMALS — SIMPSON 225 



species is Ptilodus montanus Douglass, 1908, with which I find Ptilodus 

 gracilis Gidley, 1909, to be sj'-nonymous.^ The other seven species 

 are new and are dias^nosed below. They are named for students and 

 collectors of the American Paleocene. 



Genus PTILODUS Cope 



?PTILODUS DOUGLASSI,3 new species 



Type.— U.S.N. M. no. 9795, right lower jaw with P4-M2. Col- 

 lected by A. C. Silberhng. 



Horizon and locality. — Gidley Quarry (and referred specimens from 

 Silberling Quarry), Fort Union, Middle Paleocene horizon. Crazy 

 Mountain Field, Mont. 



Diagnosis. — Structurally similar to P. montanus, but P4 and M2 

 significantly smaller both absolutely and in relation to Mj. Length 

 of P4 (mean of 3 specimens) 6.6 mm. Length of Mi (type) 3.7 mm. 

 Length of M2 (type) 2 mm. Katio length P4 : length Mi (type) 1.8. 

 Ratio length Mi : length M2 (type) 1.8. Serrations of P4 13 in known 

 specimens. 



7PTILODUS GIDLEYI,< new species 



Type.— V.S.'N.M. no. 9763, left lower jaw with P4 and broken Mi. 

 Collected by A. C. Silberling. 



Horizon and locality. — Gidley Quarry, Fort Union, Middle Pale- 

 ocene horizon. Crazy Mountain Field, Mont. 



Diagnosis. — Close to P. montanus in proportions and structure, 

 but P4 and Mi significantly smaller. Mi significantly smaller relative 

 to P4 than in P. trovessartianus or ?P. douglassi. Length P4 6.1 mm 

 (to 5.9 in referred specimen). Length AIi 2.5 mm. Ratio length P4 : 

 length Ml 2.4. Serrations of P4 14 in known specimens. 



7PTILODUS SINCLAIRI.s new species 



Type.— v. S.N. M. no. 9770, left lower jaw with P4-M2. Col- 

 lected by A. C. Silberling. 



Horizon and locality. — Gidley Quarry (and referred specimens 

 from Silberhng Quarry), Fort Union, Middle Paleocene horizon, 

 Crazy Mountain Field, Mont. 



Diagnosis. — Significantly smaller than any possibly related species 

 except lEctypodus silberlingi (diagnosed below) and Parectypodus 

 iardus (from which it differs in the presence of P3). Length P4, 

 16 specimens, 2.5-3.7 mm, mean 3.1 mm, type 3.3 mm. Length 

 Ml, 8 specimens, 1.7-2 mm, mean 1.9 mm, type 1.7 mm. Length 

 M2, 5 specimens, 0.9-1.1 mm, mean 1 mm, type 0.9 mm. Ratio 

 length P4 : length Mi, 8 specimens, 1.3-2, mean 1.6, type 1.9. Ser- 



2 It was, in any event, a homonym of Ptilodus gracilis (Cope) Osborn, 1S93, and was replaced by Ptilodus 

 admirabilis Hay, 1930, which is also added to the synonymy of P. montanus. 

 > Named for the late Earl Douglass, discoverer of the Crazy Mountain Field. 

 * Named for the late Dr. J. W. Gidley, of the U. S. National Museum. 

 « Named for the late Prof. W. J. Sinclair for his work oa the Puerco, Torrejon, and Clark Fork, 



